1. Field of the Invention
The present invention relates generally to video displays, and more specifically to a design for a cathode ray tube.
2. Description of the Prior Art
Since the inception of television, work has been performed on a nearly constant basis to improve the quality of the displayed image. In recent years, much attention has been directed to efforts to put more information, i.e. an increased number of pixels, onto the screen. This is especially true with respect to high definition television (HDTV), and computer system graphics displays.
In order to increase the number of pixels contained in a raster display, such as a television or a computer monitor, it is necessary to increase the number of scan lines and the number of pixels-width displayed on each line. Since the screen refresh rate remains fixed for television displays, and must be kept high enough to avoid flicker on computer displays, it is necessary to provide faster scanning speeds for the electron gun used to paint the raster display. For color displays, the three grouped RGB guns are subject to the same requirements. Faster scanning speeds for the electron gun reduces the time available for the gun to paint each pixel in the display.
An increased scanning rate, in turn, decreases the brightness of the image. This decrease in brightness can be compensated to some degree by increasing the voltage used to drive the electron guns. Higher voltage increases the energy of the electron beam at the phosphor, causing it to glow more brightly. However, the electron beam energy cannot simply be increased without limit. Increasing the energy has several drawbacks, including blooming effects of the scans, and increased diameter of the beam.
Another approach to increasing display brightness requires utilization of brighter phosphors on the screen. This approach also has limits, in that the brightness of the phosphors cannot be increased arbitrarily and without limits. In addition, brighter phosphors tend to be significantly more expensive.
Brightness limits caused by high scanning rates have adversely impacted the development of technologies such as high definition television. It is well known that current technologies for displaying HDTV signals generally suffer from a dramatic decrease in image brightness. Specialty, high-density computer-graphics monitors suffer from a similar scan-rate problem.
It would be desirable to provide a display tube for use with television or other information displays which provides high brightness levels combined with high information density. It would further be desirable for such a display to be easily manufacturable at a relatively low cost.